Synovial hyperplasia is a central event in the pathogenesis of bone and cartilage destruction in rheumatoid arthritis. This project is based on the hypothesis that synovial lining hyperplasia is due in part to an increase in the recruitment and activation of mesenchymal stem cells (MSC). The proposed studies will determine whether upon migration into the synovium, MSC phenotype and function, are affected by cytokines and growth factors that are produced as part of the synovial inflammatory process.